The present invention relates to an electronic lock.
Electronic locks have many advantages over entirely mechanical locks. For example, electronic locks used in combination with a microprocessor or a computer can be programed to control the electronic lock by time of day, by authorization codes, or other factors that may be programed into the processor. When a key is lost, instead of replacing the electronic lock, the electronic lock may be reprogrammed to accept a different identification code from a different key.
However, electronic locks suffer from a number of drawbacks. First, the locks require a source of power. If the power source is provided within the lock, such as in the form of a battery, then the power supply occupies space within the lock, making the lock larger. Such batteries may also be prone to corrosion which can affect the internal parts of the lock. In addition, if the battery loses power, then the lock may no longer be able to function. Further, the lock must be accessed periodically in order to change the battery. Providing power from a standard electrical power line is an alternative, but requires providing wiring to the lock. Further, such wiring may not be available in some environments, such as a desk or cabinet.
It is also desired to make the locks as small as possible, so that the electronic lock may be installed in place of an existing mechanical lock. Conventional mechanical locks used with desks or cabinets are relatively small. Thus, the space available within such a lock is confined, limiting the size and number of components that may be used within a lock.
In particular, it is desired to replace a mechanical lock having a replaceable or interchangeable core, such as those described in U.S. Pat. Nos. 3,206,959, 4,294,093 and 5,136,869. Such locks are sometimes referred to as “interchangeable core” locks. However, a problem arises due to the elongate throw pins used with such interchangeable core locks. The lock must be capable of accepting the pair of elongate throw pins which are used to throw a secondary locking mechanism such as a bolt to which the lock is attached. Accommodating elongate throw pins further restricts the space available within the lock.
Another difficulty with electronic locks is that they are susceptible to opening in response to sharp blows. Typically, electronic locks use a solenoid. However, it is often possible to jar a solenoid plunger so that an electronic lock may be opened by applying a sharp force to the lock, such as striking a lock with a hammer.
Another problem with electronic locks is that often a solenoid is used to move a plunger into and out of interfering relationship with the internal cylinder and the external shell. This may result in several problems. First, the solenoid and its plunger must be constructed to withstand the primary force directed on the plunger when a person attempts to rotate the cylinder when locked. Another problem is that the electronic lock may be difficult to lock, since it may be difficult to align the plunger with its corresponding bore. If the plunger does not align properly with the bore, the plunger cannot enter the bore so as to interfere with the movement of the cylinder.
Another difficulty is that the lock must be protected from being opened by an externally applied magnetic field. Where the lock has moving parts made of steel or other ferrous material, it may be possible to open the lock without the key by applying a large external magnetic field to the lock. In particular, where a solenoid is used, the solenoid plunger must be prevented from being moved out of locking position by an externally applied magnetic field.
Yet another problem is that some electronic locks allow removal of the key during rotation of the lock. In that event, a person may forget to return the cylinder to its locked position after the lock has been opened.
Accordingly, what is therefore desired is an electronic lock that occupies a small volume, that may be used to replace existing mechanical locks (including interchangeable core locks), that does not require a power source inside of the lock or external wiring, that is not susceptible to being opened in response to tampering (including tampering by means of an externally applied magnetic field), that may be consistently returned to a position that allows secure locking, and that prevents withdrawal of a key during operation.